1. Field of the Invention
The invention concerns a device for determining the position of an elevator car, including a device permanently installed in the elevator shaft which is at least as long as the total travel of the car between its uppermost and lowermost stop positions, and an additional device installed on the elevator car.
Devices of this type are used in elevator systems of various kinds. In these elevator systems, an elevator car is moved vertically between the floors of a building, and it is necessary to know the present position of the elevator car. Switching devices installed in the elevator shaft have a role in this.
2. Description of the Related Art
U.S. Pat. No. 4,427,095 describes a device for determining the position of an elevator car, in which a coded tape is scanned by a tape reader. Each position of the elevator car corresponds to a certain code value, which is evaluated by a microprocessor.
U.S. Pat. No. 6,142,259 describes a device for controlling a hydraulic elevator, in which an automatic control system for the elevator receives information about changes in the position of the elevator car by elevator shaft pulse generators. However, the travel of the elevator car is also monitored by a flowmeter, which makes it possible to regulate the speed.
U.S. Pat. No. 6,510,923 describes a device for controlling a hydraulic elevator, in which a flowmeter is not used. Instead, a pressure sensor installed in this line determines the pressure in the cylinder line. The change in pressure with respect to time is evaluated, and it is also stated that the acceleration of the elevator car can be computed from the pressure. From this information, it is then supposed to be possible to derive the speed of the elevator car and the distance it has traveled. It seems questionable whether the accuracy of the pressure sensors is great enough to allow sufficiently exact control of an elevator from the change in pressure as a function of time and from repeated differentiation of this data.
EP-A1-1 158 310 describes a device for determining the position of an elevator car, in which a sonic signal conductor is installed in the elevator shaft, and a signal coupler is installed on the elevator car. The sonic signal is in the ultrasonic range. The sonic signal conductor consists of a magnetostrictive metallic material. This system requires a transmitting unit with a signal generator and the aforementioned signal coupler, as well as at least one signal receiver and one evaluation unit.